Develop Reference

Save entire model but load weights only

I have defined a deep learning model my_unet() in tensorflow. During training I set save_weigths=False since I wanted to save the entire model (not only the wieghts bu the whole configuration). The generated file is path_to_model.hdf5.
However, when loading back the model I used the earlier version (I forgot to update it) in which I first called the model and then load the model using:
model = my_unet()
model.load_weights(path_to_model.hdf5)
Instead of simply using: model = tf.keras.models.load_model(path_to_model.hdf5) to load the entire model.
Both ways of loading the model and the weights provided the same predictions when run in some dummy data and there were no errors.
My question is: Why loading the entire model using model.load_weights() does not generate any problem? What is the structure of the hdf5 file and how theese two ways of loading exactly work? Where can I find this information?

You can please see the documentation here for any future reference: http://davis.lbl.gov/Manuals/HDF5-1.8.7/UG/03_DataModel.html

How can I "see" the model/network when loading a model from tfhub?

I'm new to this topic, so forgive me my lack of knowledge. There is a very good model called inception resnet v2 that basically works like this, the input is an image and outputs a list of predictions with their positions and bounded rectangles. I find this very useful, and I thought of using the already worked model in order to recognize things that it now can't (for example if a human is wearing a mask or not). Yes, I wanted to add a new recognition class to the model.
import tensorflow as tf
import tensorflow_hub as hub
mod = hub.load("https://tfhub.dev/google/faster_rcnn/openimages_v4/inception_resnet_v2/1")
mod is an object of type
tensorflow.python.training.tracking.tracking.AutoTrackable, reading the documentation (that was only available on the source code was a bit hard to understand without context)
and I tried to inspect some of it's properties in order to see if I could figure it out by myself.
And well, I didn't. How can I see the network, the layers, the weights? the fit methods, Is it's all abstracted away?. Can I convert it to keras? I want to experiment with it, see if I can modify it, and see if I could export the model to another representation, for example pytorch.
I wanted to do this because I thought it'd be better to modify an already working model instead of creating one from scratch. Also because I'm not good at training models myself.

I've run into this issue too. Tensorflow hub guide says:
This error frequently arises when loading models in TF1 Hub format with the hub.load() API in TF2. Adding the correct signature should fix this problem.
mod = hub.load(handle).signatures['default']
As an example, you can see this notebook.

You can dir the loaded model asset to see what's defined on it
m = hub.load(handle)
dir(model)
As mentioned in the other answer, you can also look at the signatures with print(m.signatures)
Hub models are SavedModel assets and do not have a keras .fit method on them. If you want to train the model from scratch, you'll need to go to the source code.
Some models have more extensive exported interfaces including access to individual layers, but this model does not.

Improving a pre-trained tensorflow object detection model

I want to use tensorflow for detecting cars in an embedded system, so I tried ssd_mobilenet_v2 and it actually did pretty well for me, except for some specific car types which are not very common and I think that is why the model does not recognize them. I have a dataset of these cases and I want to improve the model by fine-tuning it. I should also note that I need a .tflite file because I'm using tflite_runtime in python.
I followed these instructions https://github.com/EdjeElectronics/TensorFlow-Object-Detection-API-Tutorial-Train-Multiple-Objects-Windows-10 and I could train the model and reached a reasonable loss value. I then used export_tflite_ssd_graph.py in the object detection API to build inference_graph from the trained model. Afterwards I used toco tool to build a .tflite file out of it.
But here is the problem, after I've done all that; not only the model did not improve, but now it does not detect any cars. I got confused and do not know what is the problem, I searched a lot and did not find any tutorial about doing what I need to do. They just added a new object to a model and then exported it, which I tried and I was successful doing that. I also tried to build a .tflite file without training the model and directly from the Tensorflow detection model zoo and it worked fine. So I think the problem has something to do with the training process. Maybe I am missing something there.
Another thing that I did not find in documents is that whether is it possible to "add" a class to the current classes of an object detection model. For example, let's assume the mobilenet ssd v2 detects 90 different object classes, I would like to add another class so that the model detects 91 different classes instead of 90 classes. As far as I understand and tested after doing transfer learning using object detection API, I could only detect the objects that I had in my dataset and the old classes will be gone. So how do I do what I explained?

I found out that there is no way to 'add' a class to the previously trained classes but with providing a little amount of data of that class you can have your model detect it. The reason is that the last layer of the model changes when transfer learning is applied. In my case I labeled around 3k frames containing about 12k objects because my frames would be complicated. But for simpler tasks as I saw in tutorials 200-300 annotated images would be enough.
And for the part that the model did not detect anything it has something to do with the convert command that I used. I should have used tflite_convert instead of toco. I explained more here.

keras problems loading custom model from yolov2

I've searched around for a couple of answers regarding the load_model from keras but I still have a question.
I am following this model really closely (https://github.com/experiencor/keras-yolo2), and am training on a custom dataset.
I have done the training which gives me a yolov2.h5 file, basically model weights to fit into the keras model. But I am encountering some problems with the loading of the model.
After loading the model (in a separate.py file)
model = load_model('file_dir/yolov2.h5')
First I encounter the issue
NameError: name 'tf' is not defined
Which I then searched up to modify my code to add custom objects as such:
model = load_model('file_dir/yolov2.h5', custom_objects={'tf':tf})
This clears the first error but results in another
ValueError: Unknown loss function : custom_loss
I used the custom_loss function from the yolov2 (https://github.com/experiencor/keras-yolo2/blob/master/frontend.py), so i tried to solve it by
from frontend import YOLO
model = load_model('file_dir/yolov2.h5' custom_objects={'tf':tf, 'custom_loss':YOLO.custom_loss)
But ran into another error:
TypeError: custom_loss() missing 1 required positional argument
I got rather stuck here because I have no idea how to fit in the parameters for custom_loss. Seek some help regarding this (Don't particularly understand this part since I'm loading my model in a different python script separate.py). Thank you so much!
(Edit: This fix doesn't work for me either)
model = load_model('file_dir/yolov2.h5', compile = False)

To resolve this problem, as you already have the network at hand, only save trained weights (like what keras trainer does in callback).
For testing, make model, no need to compile, and then load trained weights using model.load_weights(path/to/saved/weights).
You also can use "by_name=True" if you make the network in a different way, this time you should keep layer names.
Another option id to manually set weights; for this you will load .h5 file bu "h5py" (h5py.File(path/to/weights, mode='r')) for example (have look how keras do that), then try to correspond layer names of the model and loaded weights.

Unable to load and use multiple keras models

I'm trying to load three different models in the same process. Only the first one works as expected, the rest of them return like random results.
Basically the order is as follows:
define and compile first model
load trained weights before
rename layers
the same process for the second model
the same process for the third model
So, something like:
model1 = Model(inputs=Input(shape=input_size_im) , outputs=layers_firstmodel)
model1.compile(optimizer='sgd', loss='mse')
model1.load_weights(weights_first, by_name=True)
# rename layers but didn't work
model2 = Model(inputs=Input(shape=input_size_im) , outputs=layers_secondmodel)
model2.compile(optimizer='sgd', loss='mse')
model2.load_weights(weights_second, by_name=True)
# rename layers but didn't work
model3 = Model(inputs=Input(shape=input_size_im) , outputs=layers_thirdmodel)
model3.compile(optimizer='sgd', loss='mse')
model3.load_weights(weights_third, by_name=True)
# rename layers but didn't work
for im in list_images:
results_firstmodel = model1.predict(im)
results_secondmodel = model2.predict(im)
results_thirdmodel = model2.predict(im)
I'd like to perform some inference over a bunch of images. To do that the idea consists in looping over the images and perform inference with these three algorithms, and return the results.
I have tried to rename all layers to make them unique with no success. Also I created a different graph for each network, and with a different session do the inference. This works but it's very inefficient (in addition I have to set their weights every time because of sess.run(tf.global_variables_initializer()) removes them). Each time it's created a session tensorflow prints "creating tensorflow device (/device:GPU:0)".
I am running Tensorflow 1.4.0-rc0, Keras 2.1.1 and Ubuntu 16.04 kernel 4.14.

The OP is correct here. There is a serious bug when you try to load multiple weight files in the same script. The above answer doesn't solve this. If you actually interrogate the weights when loading weights for multiple models in the same script you will notice that the weights are different than when you just load weights for one model on its own. This is where the randomness is the OP observes coming from.
EDIT: To solve this problem you have to encapsulate the model.load_weight command within a function and the randomness that you are experiencing should go away. The problem is that something weird screws up when you have multiple load_weight commands in the same script like you have above. If you load those model weights with a function you issues should go away.

From the Keras docs we have this explanation for the user of load_weights:
loads the weights of the model from a HDF5 file (created by save_weights). By default, the architecture is expected to be unchanged. To load weights into a different architecture (with some layers in common), use by_name=True to load only those layers with the same name.
Therefore, if your architecture is unchanged you should drop the by_name=True or make it False (its default value). This could be causing the inconsistencies that you are facing, as your weights are not being loaded probably due to having different names on your layers.
Another important thing to consider is the nature of your HDF5 file, and the way you created it. If it indeed contains only the weights (created with save_weights as the docs point out) then there should be no problem in proceeding as explained before.
Now, if that HDF5 contains weights and architecture in the same file, then you should be loading it with keras.models.load_model instead (further reading if you like here). If this is the case then this would also explain those inconsistencies.
As a side suggestion, I prefer to save my models using Callbacks, like the ModelCheckpoint or the EarlyStopping if you want to automatically determine when to stop training. This not only gives you greater flexibility when training and saving your models (as you can stop them on the optimal training epoch or when you desire), but also makes loading those models easily, as you can simply use the load_model method to load both architecture and weights to your desired variable.
Finally, here is one useful SO post where saving (and loading) Keras models is explained.